The Study Of Preparation And Reaction Performance Of Modified Al₂O₃ Isomerization Catalyst

As an important chemical product,especially as a high quality blending component of gasoline,iso-olefin plays an important role in chemical industry and daily life.In this paper,using industrial ether-post C₅ fraction as raw material,the efficient and stable but cheap and readily available isomerization catalyst was developed to satisfy the isomerization reaction of complex raw materials and to meet the needs of large-scale industrial production.Firstly,the isomerization properties of alumina modified with boron element were investigated.The results indicated that the modification with non-metallic element B can increase the weak acid content and produce strong acid site of the catalyst surface.However,with the impregnation amount of non-metallic element B increasing,the non-metallic element B which did not react with alumina existed in the form of oxide on the surface of the catalyst,which led to the content of strong acid decreasing.The solid state reaction depth of non-metallic element B and alumina is mainly affected by calcination temperature and calcination time.Only the catalyst treated with suitable calcination condition has better isomerization performance.If the calcination temperature is high and the calcination time is long,the pore size of the catalyst decreases because the non-metallic element B grows into the bulk phase deep.Besides the catalyst would be sintered which led to the surface area decreasing.The isomerization activity of the catalyst can be improved by proper amount of the compound of B and Al.But the less the mono-phase B oxide is,the stabler the catalyst is.Thus,the content of non-metallic element B and the solid state reaction depth of B with alumina are the key factors which affect the activity of isomerization,especially for the stability of catalyst.The effects of transition metal type,impregnation amount,calcination temperature and pre-reduction temperature on the performance of the catalyst were also studied.The results showed that with the increase of metal M₄ impregnation amount,the isomerization stability increases but the isomerization activity decreases.The calcination temperature affects the depth of solid state reaction between the metal M₄and the catalyst carrier,and then affects the isomerization performance of the catalyst.The stability of the catalyst calcined at 500°C is the best.The conversion of straight alkenes would be greatly increased by raising the pre-reduction temperature.Nevertheless,only the hydrogenation by-reaction is aggravated but the selectivity of iso-olefins decreases.